TY  - JOUR
A1  - Camacho, J.P.M.
A1  - Schmid, M.
A1  - Cabrero, J.
T1  - B Chromosomes and Sex in Animals
JF  - Sexual Development
N2  - Supernumerary (B) chromosomes are dispensable elements found in many eukaryote genomes in addition to standard (A) chromosomes. In many respects, B chromosomes resemble sex chromosomes, so that a common ancestry for them has frequently been suggested. For instance, B chromosomes in grasshoppers, and other insects, show a pycnotic cycle of condensation-decondensation during meiosis remarkably similar to that of the X chromosome. In some cases, B chromosome size is even very similar to that of the X chromosome. These resemblances have led to suggest the X as the B ancestor in many cases. In addition, sex chromosome origin from B chromosomes has also been suggested. In this article, we review the existing evidence for both evolutionary pathways, as well as sex differences for B frequency at adult and embryo progeny levels, B chromosome effects or B chromosome transmission. In addition, we review cases found in the literature showing sex-ratio distortion associated with B chromosome presence, the most extreme case being the paternal sex ratio (PSR) chromosomes in some Hymenoptera. We finally analyse the possibility of B chromosome regularisation within the host genome and, as a consequence of it, whether B chromosomes can become regular members of the host genome.
KW  - A chromosomes
KW  - B chromosomes
KW  - sex ratio
KW  - X chromosome
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-196321
SN  - 1661-5425
SN  - 1661-5433
N1  - This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
VL  - 5
IS  - 3
ER  - 
TY  - JOUR
A1  - Lamatsch, D. K.
A1  - Trifonov, V.
A1  - Schories, S.
A1  - Epplen, J. T.
A1  - Schmid, M.
A1  - Schartl, M.
T1  - Isolation of a Cancer-Associated Microchromosome in the Sperm-Dependent Parthenogen Poecilia formosa
JF  - Cytogenetic and Genome Research
N2  - In the asexual all-female fish species Poecilia formosa, the Amazon molly, supernumerary chromosomes have frequently been found in both laboratory-reared and wild-caught individuals. While wild-caught individuals with B chromosomes are phenotypically indifferent from conspecifics, individuals carrying B chromosomes from recent introgression events in the laboratory show phenotypic changes. Former analyses showed that the expression of a pigment cell locus is associated with the presence of these B chromosomes. In addition, they contain a so far unidentified locus that confers a higher susceptibility to tumor formation in the presence of pigmentation pattern. Isolation by microdissection and hybridization to metaphase chromosomes revealed that they contain one or several sequences with similarity to a highly repetitive pericentromeric and subtelomeric sequence in A chromosomes. Isolation of one particular sequence by AFLP showed that the B chromosomes contain at least 1 copy of an A-chromosomal region which is highly conserved in the whole genus Poecilia, i.e. more than 5 million years old. We propose it to be a single copy sequence.
KW  - paternal introgression
KW  - AFLP
KW  - asexual reproduction
KW  - B chromosomes
KW  - gynogenesis
KW  - microdissection
KW  - telomeres
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-196785
SN  - 1424-8581
SN  - 1424-859X
N1  - This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
VL  - 135
IS  - 2
ER  -